Università degli Studi di Pavia

Centro Interdisciplinare di Bioacustica e Ricerche
Ambientali

Ziphius cavirostris is a pelagic, deep-diving
species and the only beaked whale commonly found in the
Mediterranean Sea. The species was described by G. Cuvier,
as a fossil, using a partial skull collected in 1803 near
Fos-sur-Mer, on the Mediterranean coast of France (Cuvier,
1823). Beaked whales generally live offshore often
associated with regions characterized by canyons or steep
escarpments.
In recent years, sightings of Z. cavirostris
have been reported more frequently in some areas, such as
the Ligurian Sea, where studies concerning habitat use and
diving behaviour were also carried out (Azzellino et al.,
2003; Johnson et al., 2004).
In recent years, mass strandings of this species appeared
to be associated with naval activities with use of high
power sonars (Simmonds and Lopez-Jurado, 1991; D’Amico
(ED), 1998; Frantzis, 1998 and 2004; Evans and England,
2001; Martín, 2002; Freitas, 2004; Martín et
al., 2004, Fernàndez et al., 2004).

Assessing and mitigating such impacts is
currently limited by the lack of scientific knowledge of
beaked whales physiology, behaviour, distribution, and
habitat use. A keypoint in mitigation strategies is the
ability to detect the animals, by either visual of
acoustic observations, or by both. CIBRA is mainly
interested in developing and tuning PAM (Passive Acoustic
Monitoring) equipment and software to make the acoustic
detection of beaked whales possible and efficient.

Acoustic detection of Cuvier's beaked
whales

Z. cavirostris is an elusive
species whose acoustic signals remained unknown till last
year when a team of Woods Hole Oceanographic Institution,
headed by Peter Tyack, attached a sophisticated recording
tag on the back of several animals. The tag, named D-TAG,
attached by suction caps, is able to record the movements
of the animal together with the sounds it receives and the
sounds it emits. For the first time it was possible to
record their sounds and to characterize the Z.cavirostris
diving profile. The results clearly explain why those
sounds have been never recorded with hydrophones deployed
close to the sea surface.

Z.cavirostris emits sounds only
at depths greater than 400-500 meters; the sounds are
short ultrasonic pulses centered at about 40 kHz (range
20-60 kHz) and emitted with at intervals of about 400ms.
As they are high in frquency and emitted at great depth,
they reach the sea surface with very little energy and are
impossible to detect with standard gear working up to 20
kHz only.

The aim of our study was to broaden the
knowledge related to Cuvier’s beaked whales, to
characterize their habitat, and to remotely record their
acoustic signals by developing suitable equipment.

In late September 2005 CIBRA carried out
a bio-acoustic survey during an extensive NURC (NATO
Undersea Research Center, La Spezia, IT) research campaign
(Zifio ’05) in the Ligurian Sea. The CIBRA team was on
board a 12 meter catamaran, named Krill, with its own
equipment based on a high quality towed array equipped
with a newly designed low-noise front-end featuring
digital recording and real-time spectrographic displaying
with a nearly 90 kHz bandwidth.
During the cruise, two animals were sighted immediately
before diving. No other animals were observed before and
after this sighting. The boat was stopped and the engines
turned off. The array sank more than 40 meters, but still
not in a vertical stand due to strong drifting conditions.
A few minutes after the animals started diving, high
frequencies click trains were noticed on the real-time
spectrograms (SeaProUltra, two channels, 96 kHz
bandwidth). Later analyses on the recorded files showed
click series with features matching the description given
by Johnson et al., 2005.
Frequency center, bandwidth, waveform, repetition
intervals and amplitude variations related to head
scanning movements confirm that recordings captured the
emissions of two Ziphius cavirostris.
This result is relevant for setting up equipment needed
for mitigation procedures where the presence of Cuvier’s
beaked whales must be estimated and to monitor critical
habitats for this species.

This cruise was carried out within the NURC - NATO
Undersea Research Center SOLMAR project. We acknowledge
ONR Office of Naval Research for having funded the
development of the equipment. NURC website:
http://nurc.nato.int ; SOLMAR website
http://solmar.nurc.nato.int

Much of the current knowledge of this
species has been derived from stranding data.
Historically, stranding data in the Mediterranean Sea has
been collected by individual researchers, and more
recently, over the last two decades, by national stranding
networks. In cooperation with the Natural History Museum
of Milan and other organizations, an extensive review of
stranding data collected by stranding networks from Italy,
Greece, Spain, and France has been made. Results were
completed with information gleaned from the literature,
personal communications, regional newspapers, and the
world wide web from the countries that border the
Mediterranean Sea. While this review is certainly not
exhaustive, it has allowed the creation of an extensive
geo-referenced basin wide database using a geographic
information system (GIS) of over 300 stranding events. The
acquired data permit documentation of the number of mass
stranding events, allow general observations about
distribution and chronology of stranding events dating
back to 1803, and enables evaluation of strandings based
on several different criteria.

This paper has been published on a
Special Issue of the Journal of Cetacean Research and
Management entirely concerned with Beaked whales.

The research project has been developed
in coordination with the NATO Underwater Research Center (SOLMAR Project), with the
cooperation of the Italian
Navy, of the SPAWAR Center (San Diego, US), of the
Natural History Museum of Milan (Italy) and of the Centro Studi Cetacei (CSC).

GIS map of strandings of Ziphius cavirostris
recorded in the Mediterranean Sea since 1803.
Strandings of two animals are marked in yellow; mass
strandings of three or more animals are marked in red.